#define _CRT_SECURE_NO_WARNINGS	

#include<stdio.h>

int main()
{
    double q;
    scanf("%lf", &q);
    double s = 0;
    double n = 0;
    while (s < q)
    {
        n++;
        s += (n + 1) / n;
    }
    printf("%.6f", s - (n + 1) / n);
    return 0;
}